The clipping you are seeing at the top is normal for the Lightroom CC histogram. It may clip very tall spikes vertically so that you can see significant data in the other areas. Lightroom Classic and Camera Raw's histograms behave similarly.

That's a screenshot from Lightroom Classic rather than Lightroom CC. I'm guessing you want to click the triangles to show the clipping warnings? It doesn't work quite the same way in Lightroom CC, but hold down the Alt/Opt key while moving the Light panel sliders to see clipping warnings.